1. Field of the Invention
This invention relates to a method for the production of a sintered lithium titaniumphosphate which is usable as a highly lithium ion conductive inorganic solid electrolyte and a sintered pellet obtained by this method. Such an electrolyte is particularly useful as an inorganic solid electrolyte for cells such as lithium ion cells.
2. Description of the Prior Art
The lithium ion cells currently used in such portable electronic devices as portable telephones are advantageous over other sorts of cells in terms of energy density. Lithium ion cells are therefore being developed for power storage and for use as the power source for electric cars. Organic electrolytic solutions are used as electrolytes in the cells of rechargeable lithium ion batteries now available on the market. They have such problems so possible leakage and corrosion and also of being combustible.
Among the lithium ion conductive materials which are prospective alternative substances for the organic electrolytic solutions is counted lithium titaniumphosphate [LiTi.sub.2 (PO.sub.4).sub.3 ], which is an inorganic solid electrolyte. This is a chemically and electrochemically safe material as compared with organic electrolytic solutions and is thought to be a promising material for practical use. However, the inorganic electrolytes have a disadvantage in that it must be formed into a sintered pellet, necessitating a multistage, time-consuming process which comprises mixing raw material powders, firing the resultant mixture, further molding the fired mixture in the shape of tablets, and sintering the produced tablets. In addition, the firing treatment has to be conducted at a high temperature in the approximate range of 1000-1200.degree. C. (H. Aono, E. Sugimoto, Y. Sadaoka, N. Imanaka, and G. Adachi; J. Electrochem. Soc., 137 (1990), 1023; referred to hereinafter as "cited reference 1"). A method which is capable of easily manufacturing the electrolyte by a quick one-stage process at a low temperature has therefore been desired.
In light of the foregoing circumstances, this invention is directed to providing a novel method that permits easy production of a sintered lithium titaniumphosphate as a highly lithium ion conductive inorganic solid electrolyte and a sintered pellet obtained by the method.